Glass color filter for use under daylight color fluorescent light

ABSTRACT

A GLASS COLOR FILTER SUITABLE FOR USE IN COLOR PHOTOGRAPHY UNDER DAYLIGHT COLOR FLUORESCENT LIGHT IS PREPARED FROM A GLASS COMPOSITION COMPRISING 100 PARTS OF BASE GLASS COMPOSED OF, BY WEIGHT, 50-70% SILICIC ACID ANHYDRIDE, 817% LEAD OXIDE, 13-23% OF EITHER ONE OR BOTH OF SODIUM OXIDE AND POTASSIUM OXIDE, 3-12% OF EITHER ONE OR BOTH OF CALCIUM OXIDE AND MAGNESIUM OXIDE. AND 0.2-0.5% ARSENIC OXIDE, AND A COLORING AGENT COMPOSED OF, BY WEIGHT, 2.0-4.0% CERIUM OXIDE, 2.5-5.0% TITANIUM OXIDE, 0.001-0.02 NICKEL OXIDE, 0.8-2.2% MANGANESE DIOXIDE, AND 0.3-2.5% NEODYMIUM OXIDE.

Dec. 19, 1972 SPECTRAL ENERGY SPECTRAL TRANSMITTANCE TAKASHI MATSUURA ETAL 3,706,638

GLASS COLOR FILTER FOR USE UNDER DAYLIGHT COLOR FLUORESCENT LIGHT FiledSept. 20, 1971 FIG] WAVE LENGTH (m p) F IGZ WAVE LENGTH (mp) UnitedStates Patent 3,706,688 GLASS COLOR FILTER FOR USE UNDER DAY- LIGHTCOLOR FLUORESCENT LIGHT Takashi Matsunra and Mitsuo Chikano, Tokyo,Japan, assignors to Hoya Glass Works, Tokyo, Japan Filed Sept. 20, 1971,Ser. No. 181,782

Claims priority, application Japan, Sept. 18, 1970, 45/551,805

Int. Cl. F21v 9/.00; C03c 3/10, 3/30 US. Cl. 252300 Claim ABSTRACT OFTHE DISCLOSURE A glass color filter suitable for use in colorphotography under daylight color fluorescent light is prepared from aglass composition comprising 100 parts of base glass composed of, byweight, 50-70% silicic acid anhydride, 8- 17% lead oxide, 1323% ofeither one'or both of sodium oxide and potassium oxide, 3-12% of eitherone or both of calcium oxide and magnesium oxide, and 0.20.5% arsenicoxide, and a coloring agent composed of, by weight, 2.0-4.0% ceriumoxide, 2.5-5.0% titanium oxide, 0.00l0.02 nickel oxide, 0.8-2.2%manganese dioxide, and 0.32.5% neodymium oxide.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This inventionrelates to a glass color filter for use in taking color photographsunder a daylight color fluorescent light.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, FIG. 1is a diagram showing the spectral energy distribution curves ofsunlight, electric light, and daylight color fluorescent light; and FIG.2 is a diagram showing the spectral transmittance curves of the colorglass filter of the present invention and a gelatin filter. I

DESCRIPTION OF THE INVENTION As shown in FIG. 1, the spectral energydistribution curve 1 of the daylight color fluorescent light difiersgreatly from the spectral energy distribution curve 2 of sunlight, andexperience tells that when a color photograph is taken under theillumination of daylight colorfluores- 3,706,688 Patented Dec. 19, 1972spectra in thevicinity of 400, 450, 550 and 580 me. This indicates'thata simple color temperature converting filter does not serve to givecorrect color reproduction.

Gelatin filters for correcting colors in color photography under adaylight color fluorescent lamp have previously been proposed (see curve4 in FIG. 2). However, color correction with such gelatin filters is notsuflicient, and there are defects such as poor flatness caused by thelamination of a plurality of filter elements, or marked color fadingbecause of its organic nature. On the other hand, it has been consideredimpossible to produce glass filters having such a spectral transmittancecurve.

We have derived the spectral transmittance curve of an ideal colorfilter from the spectral energy distribution of daylight colorfluorescent light and the spectral sensitivitycurve of a daylight-typecolor photographic film, and also made extensive work on glass coloringagents. This finally led to successful production of a stable glasscolor filter which is free from color fading and has superior colorreproducibility as compared with the gelatin filter.

In FIG. 2, curve 4 shows the spectral transmittance of a gelatin filterwhich is considered to show good color reproduction when used in takingcolor photographs of the daylight type under the illumination of adaylight color fluorescent lamp. We have examined the spectral energydistribution of daylight color fluorescent light and the spectralsensitivity of a daylight type color photographic film so as todetermine the spectral transmittance curve of an ideal color filter. Asa result, we have found that the color reproduction in color photographyis markedly improved by reducing the transmittance of the filter at theblue region (400500 m and the green region (500-600 mp) stepwise withoutreducing the transmittance at the red region (600-700 my.) as much aspossible, and sharply reducing the energy distribution and the brightline spectrum in the vicinity of 580 m of a daylight color fluorescentlamp as shown by curve 1 of FIG. 1.

However, a combination of glass coloring compounds which meets theserequirements on the spectral transmittance curve has not been known. Wehave made extensive studies on the combination of glasscoloring-compounds and consequently found that the transmittance in thevicinity of 580 m can be sharply reduced selectively by absorbing theultraviolet region through cerium oxide and titanium oxide, reducing thetransmittance at the blue and green regions through manganese dioxideand nickel oxide, and allowing neodymium oxide to be copresent withmanganese oxide. Hence, the presentinvention specifies glass ingredientsmost suitable for a color filter which is intended for use in takingdaylight-type color photographs under the illumination of a daylightcolor fluorescent lamp.

According to the present invention, there is provided a glass graphcolor filter comprising 100 parts of base glass composed of, by weight,5070% silicic acid anhycent lamp without using a color filter, theresulting color dride (SiO 8-l7% lead oxide, 13-23% of either one orboth of sodium oxide (Na- O) and potassium oxide (K 0), 3-12% of eitherone or both of calcium oxide (CaO) and magnesium oxide (MgO), and0.2-0.5% arsenic oxide (As O and a coloring agent composed of, byweight, 2.0-4.0% cerium oxide -(Ce O 2.5-5.0% titaniumoxide (TiO0.001-0.0l% nickel oxide (NiO), 0.80-2.20% manganese dioxide (MnO and0.30-2.50% neodymium oxide.

' The glass filter can be prepared by melting these ingredients'andforming them into'gla'ssina customary manner."

One example of the spectral transmittance curve of the resulting filteris shown by curve in FIG. 2.

Silicic acid anhydride is a principal ingredient of the glass accordingto the present invention, If its amount is below 50%, the resultingglass has poor resistance to weather, and excessive coefiicient ofthermal expansion. If the amount exceeds 70%, the glass batch isdifficult to melt at ordinary melting operation temperatures.

. Lead oxide assists the ultraviolet absorbing ability of cerium oxideand titanium oxide added for the purpose of absorbing ultraviolet rays.If the amount exceeds 17% the red region absorptionby manganese dioxideincreases to a disadvantage. l

Sodium oxide and potassium oxide are ess'entialiti: gredients for glassformation and facilitate glass melting. If the amount is below 13%,these ingredients do not produce any significant efiect. On the otherhand, amounts above 23% cause an increase in the red region absorptionof manganese dioxide to disadvantage. 7

Calcium oxide and magnesium oxide serve to control the viscosity ofglass during the melting and processing operations and to improve theweather resistance of glass. If the amount of these ingredients is lessthan 3%, no significant effect canbe obtained. On the other hand,amounts above 12% result in excessive viscosity, and do not contributeto theimprovement of the weather resistance. v

Arsenic oxide is. added as a clarifying agent and its amount iscontrolled within the above-mentioned range depending upon the contentsof the other ingredients.

The spectral characteristics of the glass filter of the presentinvention are that the ultraviolet region is completely absorbed, thetransmittance at the red region is maximized, the transmittance at theblue and green regions are slightly reduced, and the light in thevicinity of 580 mp. is selectively absorbed. In order to impart theseproperties to glass, cerium oxide and titanium oxide are used to absorbthe ultraviolet region, manganese dioxide to absorb the green region andsome of the blue region, nickel oxide to absorb the blue region mainly,and neodymium oxide to sharply absorb the light in the vicinity of 580 mselectively. In order to obtain a constant spectral transmittance withvarying thickness of glass, the amounts of the coloring compounds shouldbe changed according to the thickness of glass within theabove-mentioned ranges. The glass filter of the invention is mounted onthe lens portion of a photographing apparatus, and glass filters ofvarious sizes should be prepared according to the type of thephotographing apparatus and the diameter of the lens used. With largersizes, the thickness of the glass must be increased; otherwise theflatness of. the filter after polish ing may be adversely afiected. t vThe invention will be described by the following examples in which allpercentages are by weight.

EXAMPLE '1 To 100 parts of base glass composed of :.v t

The mixture was melted in air at about 1400" C., and

the resulting glass was 'opticallypolishedto -a-thickness of 2.5 mm. Thespectral transmittance of the resulting glass filter was measured, andindicated as curve 5 in FIG. 2. The glass filter obtained was suitableas a glass color filter for use under a daylight color fluorescent lamp.

EXAMPLE 2 To parts of base glass composed of:

Percent Silicic acid anhydride 54.8 Lead oxide 7 14 .9 Sodium oxide 17.9 Potassium oxide 3 .0 Calcium oxide g 7.0 Magnesium oxide 2.0 Arsenicoxide 0.4

were added the following coloring components Cerium oxide 3.2 Titaniumoxide 3.8 Nickel oxide 0.01 Manganese dioxide -2.0 Neodymium oxide 1 1.8

The mixture was melted and formedv into glass in a cus-' tomary manner,and optically polished to a thicknes of .1.0 mm. The spectraltransmittance of the resulting filter was measured. It was found thatthe spectral transmittance curve of this filter resembles the curve 5shown in- FIG. 2, and the filter was suitable as a filter with smallthickness for correction of color under a daylight color fluorescentlamp.

' The mixture was melted and formed into glass, and

optically polished to a thickness of 4.0 mm. in the same way as set inExample 1. The spectral transmittance curve was measured, and found toresemble the curve 5 in FIG. 2. The resulting glass was suitable as afilter of large jthickness for color correction under a daylight colorfluorescent lamp. l a g The glass color filters obtained in theseexamples have better color reproducibility than the gelatin filter, andalso have the advantage that optical flatness can be easily obtained,and they are free from degenerationand deterioration over long periodsof time.

-Whatisclaimedis: v 1. A glass color filter foruse under daylight colorfluorescent light, said filter comprising 100 parts of baseglass-composed of, by weight, 50-70% silicic acid anhydride, 8-17%. leadoxide, 13-23% of either. one or both of sodium oxide and potassiumoxide, 342% of either one or both of calcium oxide and magnesiumoxide,and -0.2-0.5%=arsenic oxide, and a coloring agent composed of, y weight,2.0-4.0% cerium oxid 2.55.0%

5 titanium oxide, 0.001-0.02% nickel oxide, 0.8-2.2%

manganese dioxide, and 0.3-2.5% neodymium oxide.

References Cited UNITED STATES PATENTS Tillyor 106--52 Armistead 106-53Lee, Jr. et a1. 252301.4 F

Lee, Jr. et a1. 252-3014 F JAMES E. POER, Primary Examiner M. L. BELL,Assistant Examiner Us. 01. X.R. roe-s3, 47 Q

